Publications (13)9.8 Total impact
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Article: Recent Star Formation in Nearby Early-type Galaxies
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ABSTRACT: Motivated by recent progress in the study of early-type galaxies owing to technological advances, the launch of new space telescopes and large ground-based surveys, we attempt a short review of our current understanding of the recent star-formation activity in such intriguing galactic systems.10/2007; -
Article: On the origin and fate of ionised-gas in early-type galaxies: the SAURON perspective
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ABSTRACT: By detecting ionised-gas emission in 75% of the cases, the SAURON integral-field spectroscopic survey has further demonstrated that early-type galaxies often display nebular emission. Furthermore, the SAURON data have shown that such emission comes with an intriguing variety of morphologies, kinematic behaviours and line ratios. Perhaps most puzzling was the finding that round and slowly rotating objects generally display uncorrelated stellar and gaseous angular momenta, consistent with an external origin for the gas, whereas flatter and fast rotating galaxies host preferentially co-rotating gas and stars, suggesting internal production of gas. Alternatively, a bias against the internal production of ionised gas and against the acquisition of retrograde material may be present in these two kinds of objects, respectively. In light of the different content of hot gas in these systems, with slowly rotating objects being the only systems capable of hosting massive X-ray halos, we suggest that a varying importance of evaporation of warm gas in the hot interstellar medium can contribute to explain the difference in the relative behaviour of gas and stars in these two kinds of objects. Namely, whereas in X-ray bright and slowly rotating galaxies stellar-loss material would quickly evaporate in the hot medium, in X-ray faint and fast rotating objects such material would be allowed to lose angular momentum and settle in a disk, which could also obstruct the subsequent acquisition of retrograde gas. Evidence for a connection between warm and hot gas phases, presumably driven by heat conduction, is presented for four slowly rotating galaxies with CHANDRA observations.12/2006; -
Article: Two-dimensional Kinematics of a Bar and Central Disk in NGC5448
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ABSTRACT: We analyse SAURON kinematic maps of the inner kpc of the early-type (Sa) barred spiral galaxy NGC 5448. The observed morphology and kinematics of the emission-line gas is patchy and perturbed, indicating clear departures from circular motion. The kinematics of the stars is more regular, and displays a small inner disk-like system embedded in a large-scale rotating structure. We focus on the [OIII] gas, and use a harmonic decomposition formalism to analyse the gas velocity field. The higher-order harmonic terms and the main kinematic features of the observed data are consistent with an analytically constructed simple bar model, which is derived using linear theory. Our study illustrates how the harmonic decomposition formalism can be used as a powerful tool to quantify non-circular motions in observed gas velocity fields.09/2005; -
Article: Formation and evolution of S0 galaxies: a SAURON case study of NGC7332
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ABSTRACT: We present SAURON integral-field observations of the S0 galaxy NGC7332. Existing broad-band ground-based and HST photometry reveals a double disk structure and a boxy bulge interpreted as a bar viewed close to edge-on. The SAURON two-dimensional stellar kinematic maps confirm the existence of the bar and inner disk but also uncover the presence of a cold counter-rotating stellar component within the central 250 pc. The Hbeta and [OIII] emission line maps show that the ionised gas has a complex morphology and kinematics, including both a component counter-rotating with respect to the stars and a fainter co-rotating one. Analysis of the absorption line-strength maps show that NGC7332 is young everywhere. The presence of a large-scale bar can explain most of those properties, but the fact that we see a significant amount of unsettled gas, together with a few peculiar features in the maps, suggest that NGC7332 is still evolving. Interactions as well as bar-driven processes must thus have played an important role in the formation and evolution of NGC7332, and presumably of S0 galaxies in general. Comment: 12 pages, 12 figures, accepted for publication in MNRAS02/2004; -
Article: Dynamics and Central Black Hole of NGC 3377 Based on Sauron and Oasis 2D Spectroscopic Observations
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ABSTRACT: We have constrained the central black hole mass and dynamical structure of the E6 galaxy NGC 3377, using axisymmetric dynamical models based on Schwarzschild's orbit method. These models fit simultaneously two sets of 2D-kinematic constraints: i) 475 SAURON spectra, covering the inner 41" x 33" at a spatial resolution of 0.95" and ii) 153 OASIS spectra, covering the inner 4" x 2" at 0.25" resolution. The large radii constraints of SAURON help to fix the dynamical structure of NGC 3377's main body, whereas the higher resolution data from OASIS pin down the black hole mass. I will also describe what kind of improvement in the models is needed to satisfy the increased number of data (compared to the "classical" long-slit spectroscopy).12/2001; 282:201. -
Article: Probing the Stellar Populations of Early-Type Galaxies: the SAURON Survey (Invited Talk)
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ABSTRACT: Studying the role and dynamics of nuclear density waves, in the form of bars, spirals or lopsided density distributions requires the two-dimensional mapping of their kinematics. I will present evidences for the presence of such structures using new sets of observations, and particularly OASIS integral field spectrography. I will thus emphasize the importance of nuclear m=1 modes, illustrating this with newly revealed cases and original N body simulations. I will then discuss the implications of these results in the context of AGN, starburst and dynamical evolution.12/2001; 282:189. -
Article: Two-Dimensional Kinematics and Stellar Populations of Early-Type Galaxies: First Results from the SAURON Survey (Invited Talk)
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ABSTRACT: We present the SAURON project, which is aimed at studying the morphology, two-dimensional kinematics and stellar populations of a representative sample of elliptical galaxies and spiral bulges. SAURON, a dedicated integral-field spectrograph that is optimized for wide-field observations and has high throughput, was built in Lyon and is now operated at the WHT 4.2m telescope. At present, we have observed approximately two thirds of the seventy-two sample galaxies with SAURON. A comparison with published long-slit measurements demonstrates that the SAURON-data is of equal or better quality, and provides full two-dimensional coverage. The velocity and velocity dispersion fields exhibit a large variety of morphologies: from simple rotating systems to cylindrical, disky and triaxial velocity fields, bars and decoupled cores. Most of these kinematical signatures do not have counterparts in the light distribution. While some galaxies are consistent with axisymmetry, most are more complex systems than assumed previously. This suggests that the kinematical properties of nearby E/S0 galaxies do not agree with the often assumed simplistic two-family model, in which the giant non-rotating triaxial ellipticals are opposed to the fast-rotating axisymmetric faint ellipticals and S0s.12/2001; 282:179. -
Article: Scientific Potential of Enhancing the Integral-Field Spectrometer SPIFFI with a Large Detector and High Spectral Resolution
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ABSTRACT: SPIFFI is the near-infrared integral-field spectrometer for the VLT. Assisted by the SINFONI adaptive optics module, the instrument will be offered to the astronomical community in 2004. We outline the scientific rationale for infrared integral-field spectroscopy at the VLT, and specifically for the enhancement of SPIFFI with a larger detector and higher spectral resolution gratings. We give examples of a broad variety of astronomical research which will gain specifically from the high angular and spectral resolution provided by SPIFFI, including studies of high red-shift galaxies, merging galaxies, starburst galaxies, superstar clusters, galactic nuclei, extra-solar planets, and circum-stellar discs. Comment: 8 pages, LaTeX, To be published in the Proceedings of the ESO Workshop "Scientific Drivers for ESO Future VLT/VLTI Instrumentation" held in Garching, Germany, 11-15 June 200109/2001; -
Article: Velocity profiles of galaxies with claimed black holes. II. f(E,Lz) models for M32.
Monthly Notices of the Royal Astronomical Society 10/1994; 271:99-117. · 4.90 Impact Factor -
Article: Velocity Profiles of Galaxies with Claimed Black-Holes - Part One - Observations of M31 M32 NGC3115 and NGC4594
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ABSTRACT: The presence of a massive black hole has been invoked to match the observed rotation velocities and velocity dispersions at the centres of M31, M32, NGC 3115 and NGC 4594, Here we determine stellar line-of-sight velocity profiles of these galaxies, from high spatial resolution, high S/N spectra centred on the G-band, the Mg b triplet and the Ca II IR triplet. For all spectra we determine rotation velocities, V, velocity dispersions, σ, and deviations of the velocity profiles from a Gaussian shape, as quantified by the Gauss-Hermite moments h_3_,...,h_6_. Significant deviations of the velocity profiles from a Gaussian are present in all objects. The strongest deviations are asymmetries quantified by h_3_ and are found primarily along the major axis. The amplitude of h_3_ is typically |h_3_| <~ 0.15 and is correlated with V/σ. Its sign always indicates an excess of stars at low rotation velocities, and results in the mean stellar streaming velocity being lower than the mean of the best-fitting Gaussian, the quantity conventionally used to characterize rotation. The difference is ~10 per cent for M31, M32 and NGC 3115, and ~20 per cent for NGC 4594. It is thus important that models take the observed velocity profile shapes into account. We demonstrate that the observed deviations from Gaussian velocity profiles are for the most part not the result of projection and seeing convolution. We calculate the velocity profiles predicted by Tonry's model for M32, taking seeing and projection into account, but assuming the local (unprojected) velocity distributions to be Gaussian. The predicted velocity profiles are nearly Gaussian, in conflict with our data. Self-consistent dynamical models must thus be constructed to fit the observed velocity profiles. Such models should constrain the central structure quite strongly, and will hence provide improved constraints on the mass and presence of a supermassive central object.Monthly Notices of the Royal Astronomical Society 04/1994; 268:521. · 4.90 Impact Factor -
Article: IFMOS: Integral Field Multi-Object Spectrograph for NGST
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Article: The stability of axisymmetric galaxy models with anisotropic dispersions
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ABSTRACT: Axisymmetric models constructed by means of Schwarzschild's (1979) self-consistent method are discussed, with attention also given to the stability of the models. Use is made of van Albada's axisymmetric N-body program (van Albada and van Gorkum, 1977) in order to test the stability of the equilibrium models in the presence of axisymmetric perturbations. It is found that models that have a local radial velocity dispersion below a certain critical value are unstable to such perturbations. It is suspected that a generalized stability criterion for the local anisotropic velocity dispersion may exist, analogous to the result for infinitely thin disks. This stability depends only on the orbits that constitute the model and not on the fraction of retrograde stars in each orbit. The models that are stable in the presence of axisymmetric perturbations may still be unstable to barlike perturbations. Since this instability depends on the total angular momentum of the model, the fraction of retrograde stars is important. Using Vandervoort's (1982) refinement of the Ostriker-Peebles (Ostriker and Peebles, 1973) criterion, it is found that some of the models should be stable even if all stars are direct but that other models can be made stable only when a fraction of the stars is retrograde.Proceedings of the International Astronomical Union 100:285-286. -
Article: SINFONI on the nucleus of Centaurus A
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ABSTRACT: The prominent radio galaxy Centaurus A is the closest active galaxy and a prime opportunity to study the central supermassive black hole and its influence on the environment in great detail. We used the near-infrared integral field spectrograph SINFONI to measure Centaurus A's black hole mass from both stellar and gas kinematics. This study shows how the advance in observing techniques and instrumentation drive the field of black hole mass measurements, and concludes that adaptive optics assisted integral field spectroscopy is the key to identifying the effects of the active galactic nucleus on the surrounding ionised gas. The best-fit black hole mass is MBH = 4.5 (+1.7, -1.0) ̉ 107 MSun (from H2 kinematics) and MBH = 5.5 ̱ 3.0 ̉ 107 MSun (from stellar kinematics; both with 3̮ errors). This is one of the cleanest gas versus star comparisons of a black hole mass determination, and brings Centaurus A into agreement with the relation of black hole mass versus galaxy stellar velocity dispersion.
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2007
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Universiteit Leiden
- Leiden Observartory
Leiden, South Holland, Netherlands
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